Polyglutarimides are polymers containing units of the structure: ##STR1## where R.sub.1 and R.sub.2 are H or CH.sub.3 and R.sub.3 is hydrogen, alkyl, cycloalkyl, substituted alkyl, substituted cycloalkyl, aryl, substituted aryl, alkaryl, substituted alkaryl, aralkyl, substituted aralkyl, or heterocyclic. Polyglutarimides (especially those polyglutarimides were R.sub.1 and R.sub.2 are CH.sub.3 and R.sub.3 is H or methyl), are useful thermoplastics, exhibiting thermal stability, moldability, clarity, low color, reasonable toughness, and good barrier properties. It has further been known that such polyglutarimides, especially those where acid or anhydride groups present in the polyglutarimide are reacted with an alkylating or esterifying agent to reduce the acid/anhydride content to levels of about 0.5 weight percent or less, are compatible with a broad variety of polar thermoplastics, as well as serving as compatibilizers for blends of many polar polymers. Among the polar polymers are included polyesters, especially aromatic polyesters, by which is meant the polymer formed by condensation of an aliphatic glycol with an aromatic acid, such as poly(ethylene glycol) terephthalate, commonly known as poly(ethylene terephthalate), poly(butylene terephthalate), and the like.
It has more recently been found than in the blending of polyglutarimides with polar polymers having reactive terminal or pendant groups, such as amine or primary hydroxyl, that grafting occurs, probably at residual acid or anhydride groups in the polyglutarimide. For this reason, polyglutarimides maintaining all or part of the acid/anhydride groups are preferred for such blending/grafting. Blends of polyesters, such as poly(ethylene terephthalate), with a polyglutarimide where the content of acid and/or anhydride has been substantially reduced, do not appear to be chemically attached or grafted in the absence of a catalyst.
Even more recently, it has been discovered that the extent of reaction between a polyglutarimide containing a preponderance of units of the glutarimide structure where R.sub.1 =R.sub.2 =R.sub.3 =methyl and about 5 weight percent of units derived from methacrylic acid or from methacrylic anhydride with a polyamide such as polycaprolactam may be increased by the presence of small amounts of a basic catalyst, such as sodium hydroxide.
The catalysts of the reaction between hydroxylic groups in a polyester and the acid/anhydride sites in a polyglutarimide is not known to the art, nor it is obvious that a catalyst useful with polyamides in the melt would also be useful with polyesters. It is further not obvious that the resulting graft copolymer formed in higher yield will impart improved performance to the blend of graft copolymer and remaining unreacted polyester and polyglutarimide.